Ferroelectric Crystals of Globular Molecules: Cambridge Structural Database Mining and Computational Assessment

Abstract

Hybrid or organic molecular ferroelectrics hold the potential to serve as lead-free alternatives to conventional inorganic ferroelectrics. In particular, the variants composed of globular, often cage-like molecules can host attractive properties such as multiaxial ferroelectricity, Curie temperatures above room temperature, and orientationally disordered plastic mesophases, in addition to supporting low-temperature synthesis. Here, we present the results of a screening study of the Cambridge Structural Database (CSD) leading to the discovery of 54 candidate ferroelectrics, including molecular crystals and molecular salts, many of which are likely to host plastic mesophases, along with 16 previously reported ferroelectrics. With over 1.2 million entries in the CSD, the screening procedure involved many steps, including considerations of molecular geometry and size, space group, and hydrogen bonding pattern. Out of the candidate systems, many of them were identified to be likely to also host plastic mesophases due to their resemblance to highly symmetric close-packed crystal structures. The spontaneous polarization and electronic band gaps were predicted by using density functional theory. Among the candidate ferroelectrics, 17 exhibited a spontaneous polarization greater than 10 μC/cm2, with five of them being reported at room temperature.